Filter devices are known for aircraft hydraulic circuits, said devices comprising at least one cartridge filter that is separably fastened to a hydraulic block. The filter comprises a vessel that receives a filter cartridge. The vessel is screwed to the hydraulic block.
It sometimes happens that the vessel is mounted on the hydraulic block even though a cartridge has not been placed inside the vessel. When removing the filter, it can also happen that the cartridge does not come away with the vessel but remains attached to the hydraulic block, e.g. because of resistance from a gasket carried by a member internal to the block and co-operating, in service, with the cartridge.